The present invention relates to a fluid-operated bell crank clamping device. In such fluid-operated bell crank clamping devices it is essential that such devices are constructed to operate in a safe and exact manner and have an extended useful life. Experience has shown that this will depend essentially on the manner in which the axial movement of the piston and the piston rod is transmitted to the crank level of the device. This will require that the transmission of the axial movement of the piston rod onto the bell crank of the device is accomplished by a specially constructed and arranged means.
A hydraulically or pneumatically operated bell crank clamping arrangement is known in which the axial movement of the piston rod is transmitted by rigid link to the bell crank portions of the device (German Offenlegungsschrift No. 22 22 686). In this known device in which the axial movement of the piston rod is transmitted over a rigid link to the bell crank of the device there are created relatively large forces when the device is brought in the clamping position, which results in disadvantageously large loading of the different parts of the device. This, in turn, will result into excessive wear of certain parts of the device, which may lead eventually to the necessity to replace such worn parts. Such an exchange of worn parts is evidently rather time consuming especially if it requires removing of the clamping arms from its exact adjusted working position. It is therefore desirable and of great advantage during occurring breakdown of the device to leave the clamping arm in its predetermined exactly adjusted operating position so that a quick and easy replacement of the clamping device without clamping arm is possible.